Neogene and Paleocene-Maestrichtian calcareous nannofossils in sediments of the upper continental rise off New Jersey

Maestrichtian to Holocene calcareous nannofossils from two closely spaced sites on the upper continental rise some 100 miles (161 km) southeast of Atlantic City, New Jersey, were zoned in order to help date a major canyon-cutting event in the late Miocene and to delineate and correlate other hiatuses with seismic stratigraphy. Mid-middle Eocene through middle Miocene sediments (Zones CP14 to CN6) were not recovered in these holes, but nearly all other zones are accounted for. The Eocene section is described in a companion chapter (Applegate and Wise, 1987, doi:10.2973/dsdp.proc.93.118.1987). Nannofossils are generally sparse and moderately preserved in the clastic sediments of Site 604. Sedimentation rates are extremely high for the upper Pleistocene (201 m/m.y. minimum) above a hiatus calculated to span 0.44 to 1.1 Ma. The associated disconformity is correlated with local seismic reflection Horizon Pr . Sedimentation rates continue to be high (93 m/m.y.) down to a second hiatus in the upper Pliocene dated from about 2.4 to 2.9 (or possibly 3.3) Ma. The disconformity associated with this hiatus is correlated with local seismic reflection Horizon P2 and regional Reflector Blue, which can be interpreted to mark either the onset of Northern Hemisphere continental glaciation or circulation changes associated with the closure of the Central American Seaway. Sedimentation rates in the pre-glacial lower Pliocene are only about a third those in the glacial upper Pliocene. A prominent disconformity in the upper Miocene marks a major lithologic boundary that separates Messinian(?) glauconitic claystones above from lower Tortonian conglomeratic debris flows and turbidites below. The debris flows recovered are assigned to nannofossil Zones CN8a and CN7, but drilling difficulties prevented penetration of the bottom of this sequence some 100 m below the terminal depth of the hole. Correlation of the lower bounding seismic reflector (M2/Merlin?) to a drift sequence drilled on the lower rise at DSDP Site 603, however, predicts that the debris flows began close to the beginning of the late Miocene (upper Zone CN6 time) at about 10.5 Ma. The debris flows represent a major canyon-cutting event that we correlate with the beginning of the particularly severe late Miocene glaciations believed to be associated with the formation of the West Antarctic Ice Sheet. The existence of these spectacular debris flows strongly suggest that the late Miocene glacio-eustatic low stand occurred during Vail Cycle TM3.1 (lower Tortonian) rather than during Vail Cycle TM3.2 (Messinian) as originally published. Beneath a set of coalesced regional disconformities centered upon seismic reflection Horizon Au, coccoliths are abundant and in general are moderately preserved at Site 605 in a 619-m carbonate section extending from the middle Eocene Zone CP13b to the upper Maestrichtian Lithraphidites quadratus Zone. Sedimentation rates are 37 m/m.y. in the Eocene down to a condensed interval near the base (Zone CP9). A disconformity is suspected near the Eocene/Paleocene boundary. Sedimentation rates for the upper Paleocene Zone CP8 are similar to those of the Eocene, but Zones CP7 and CP6 lie within another condensed interval. The highest Paleocene rates are 67 m/m.y. down through Zones CP5 and CP4 to a major disconformity that separates the upper Paleocene from the Danian. This hiatus spans about 2.6 m.y. (upper Zone CP3 to lower Zone CP2) and corresponds to the major sea-level drop at the base of Vail Cycle TE2.1. As the most prominent break in this Paleogene section, it may correspond to seismic reflection Horizon A* of the North American Basin. Sedimentation rates from this point to the Cretaceous/Tertiary boundary drop to 11 m/m.y., still high for a Paleocene DSDP section. No major break in deposition could be detected at the Cretaceous/Tertiary boundary.

Geochemistry of marin ash layers and epiclastic rocks from the Kerguelen Plateau

Epiclastic volcanogenic rocks recovered from the Kerguelen Plateau during Ocean Drilling Program Legs 119 and 120 comprise (pre-)Cenomanian(?) claystones (52 m thick, Site 750); a Turonian(?) basaltic pebble conglomerate (1.2 m thick, Site 748; Danian mass flows (45 m thick, Site 747); and volcanogenic debris flows of Quaternary age at Site 736 (clastic apron of Kerguelen Island). Pyroclastic rocks comprise numerous Oligocene to Quaternary marine ash layers. The epiclastic sediments with transitional mid-ocean-ridge basalt (T-MORB) origin indicate weathering (Site 750) and erosion (Site 747) of Early Cretaceous T-MORB from a then-emergent Kerguelen Plateau, connected to Late Cretaceous tectonic events. The basal pebble conglomerate of Site 748 has an oceanic-island basalt (OIB) composition and denotes erosion and reworking of seamount to oceanic-island-type volcanic sources. The vitric- to crystal-rich marine ash layers are a few centimeters thick, have rather uniform grain sizes around 60 ± 40 µm, and are a result of Plinian eruptions. Crystal-poor silicic vitric ashes may also represent co-ignimbrite ashes. The ash layers have bimodal, basaltic, and silicic compositions with a few intermediate shards. The basaltic ashes are evolved high-titanium T-MORB; a few grains in a silicic pumice lapilli layer have a low-titanium basaltic composition. The silicic ashes comprise trachytic and rhyolitic glass shards belonging to a high-K series, except for a few low-K glasses admixed to a basaltic ash layer. Feldspar and clinopyroxene compositions fit the glass chemistry: high-Ti tholeiite-basaltic glasses have Plagioclase of An40-80 and pigeonite to augite clinopyroxene compositions. Silicic ashes have K-rich anorthoclase and minor Plagioclase around An20 and ferriaugitic to hedenbergitic clinopyroxene compositions. The line of magmatic evolution for the glass shards is not compatible with simple two-end member (high-Ti T-MORB and high-K rhyolite) mixing, but favors successive Ca-Mg-Fe pyroxene, Ti magnetite, and apatite fractionation, and K-rich alkali feldspar fractionation in trachytic magmas to yield rhyolitic compositions. Plagioclase fractionation occurs throughout. This qualitative model is in basic accordance with the observed mineral assemblage. However, as the time span for explosive volcanism spans >30 m.y., this basic model cannot comply with fractional crystallization in a single magma reservoir. The ash layers resulted from highly explosive eruptions on Kerguelen and, with less probability, Heard islands since the Oligocene. The explosive history starts with widespread Oligocene basaltic ash layers that indicate sea-level or subaerial volcanism on the Northern Kerguelen Plateau. After a hiatus of 24 m.y.(?), explosive magmatic activity was vigorously renewed in the late Miocene with more silicic eruptions. A peak in explosive activity is inferred for the Pliocene-Pleistocene. The composition and evolution of Kerguelen Plateau ash layers resemble those from other hotspot-induced, oceanic-island realms such as Iceland and Jan Mayen in the North Atlantic, and the Canary Islands archipelago in the Central Atlantic.

CaCO3 content, terrigenous components, foraminifera abundance and age of sediment core MD95-2006, Barra Fan, UK

Lithology, lithic petrology, planktonic foraminiferal abundances, and clastic grain sizes have been determined in a 30 m-long core recovered from the Barra Fan off northwest Scotland. The record extends back to around 45 kyr B.P., with sedimentation rates ranging between 50 and 200 cm/kyr. The abundance of ice-rafted debris indicates 16 glacimarine events, including temporal equivalents to Heinrich events 1-4. Enhanced concentrations of basaltic material derived from the British Tertiary Province suggest that the glacimarine sediments record variations in a glacial source on the Hebrides shelf margin. Glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the Rockall Trough. The results suggest that the last British Ice Sheet fluctuated with a periodicity of 2000-3000 years, in common with the Dansgaard-Oeschger climate cycle.

Tab. 1+7: Hydrochemical analyses of firn and meltwater from different "cold" snow patches

In wide areas of Northern Siberia, glaciers have been absent since the Late Pleistocene. Therefore, ground ice and especially ice wedges are used as archives for paleoclimatic studies. In the present study, carried out on the Bykovsky Peninsula, eastern Lena Delta, we were able to distinguish ice wedges of different genetic units by means of oxygen and hydrogen isotopes. The results obtained by this study on the Ice Complex, a peculiar periglacial phenomenon, allowed the reconstruction of the climate history with a subdivision of a period of very cold winters (60-55 ka), followed by a long stable period of cold winter temperatures (50-24 ka), Between 20 ka and 11 ka, climate warming is indicated in stable isotope compositions, most probably after the Late Glacial Maximum. At that time, a change of the marine source of the precipitation from a more humid source to the present North AtIantic source region was assumed. For the Ice Complex, a continuous age-height relationship was established, indicating syngenetic vertical ice wedge growth and sediment accumulation rates of 0.7 m/ky. During the Holocene optimum, ice wedge growth was probably limited due to the extensive formation of lacustrine environments. Holocene ice wedges in thermokarst depressions (alases) and thermoerosional valleys (logs) were formed after climate deterioration from about 4.5 ka until the present. Winter temperatures were warmer at this time as compared to the cooler Pleistocene. Migration of bound water between ice wedges and segregated ice may have altered the isotopic composition of old ice wedges. The presence of ice wedges as diagnostic features for permafrost conditions since 60 ka, implies that a large glacier extending over the Laptev Sea shelf did not exist. For the remote non-glaciated areas of Northern Siberia, ice wedges were established as a powerful climate archive.

Cretaceous calcareous nannofossils of ODP Leg 103 holes

Ocean Drilling Program Leg 103 recovered Lower Cretaceous sediments from the Galicia margin off the coast of Iberia. The high diversity and abundance of assemblages makes this excellent material for the study of Early Cretaceous calcareous nannofossils. With the exception of a hiatus between the upper Hauterivian and lower Barremian, nannofossil distributions form a continuous composite section from the lower Valanginian to lower Cenomanian sediments recovered at the four sites. The sedimentation history of this rifted continental margin is complex, and careful examination of the nannofossil content and lithology is necessary in order to obtain optimum biostratigraphic resolution. The Lower Cretaceous sequence consists of a lower Valanginian calpionellid marlstone overlain by terrigenous sandstone turbidites deposited in the Valanginian and Hauterivian during initial rifting of this part of the margin. Interbedded calcareous marl and claystone microturbidites overlie the sandstone turbidites. Rifting processes culminated in the late Aptian-early Albian, resulting in the deposition of a calcareous, clastic turbidite sequence. The subsequent deposition of dark carbonaceous claystones (black shales) represents the beginning of seafloor spreading, as the margin continued to subside to depths near or below the CCD. The diversity, abundance, and preservation of nannofossils within these varied lithologies differ, and an attempt to distinguish between near shore and open-marine assemblages is made. Genera used for this purpose include Nannoconus, Micrantholithus, Pickelhaube, and Lithraphidites. In this study, six new species and one new subspecies are described and documented. Ranges of other species are extended, and an attempt is made to clarify existing, yet poorly understood, taxonomic concepts. A technique in which a single specimen is viewed with both light and scanning electron microscopes was used extensively to aid in this task. In addition, further subdivisions of the Sissingh (1977) zonation are suggested in order to increase biostratigraphic resolution.

Paleomagneitc of early Cretaceous sediments from the western Central Atlantic

Drilling at Sites 534 and 603 of the Deep Sea Drilling Project recovered thick sections of Berriasian through Aptian white limestones to dark gray marls, interbedded with claystone and clastic turbidites. Progressive thermal demagnetization removed a normal-polarity overprint carried by goethite and/or pyrrhotite. The resulting characteristic magnetization is carried predominantly by magnetite. Directions and reliability of characteristic magnetization of each sample were computed by using least squares line-fits of magnetization vectors. The corrected true mean inclinations of the sites suggest that the western North Atlantic underwent approximately 6° of steady southward motion between the Berriasian and Aptian stages. The patterns of magnetic polarity of the two sites, when plotted on stratigraphic columns of the pelagic sediments without turbidite beds, display a fairly consistent magnetostratigraphy through most of the Hauterivian-Barremian interval, using dinoflagellate and nannofossil events and facies changes in pelagic sediment as controls on the correlations. The composite magnetostratigraphy appears to include most of the features of the M-sequence block model of magnetic anomalies from Ml to Ml ON (Barremian-Hauterivian) and from M16 to M23 (Berriasian-Tithonian). The Valanginian magnetostratigraphy of the sites does not exhibit reversed polarity intervals corresponding to Ml 1 to M13 of the M-sequence model; this may be the result of poor magnetization, of a major unrecognized hiatus in the early to middle Valanginian in the western North Atlantic, or of an error in the standard block model. Based on these tentative polarity-zone correlations, the Hauterivian/Barremian boundary occurs in or near the reversed-polarity Chron M7 or M5, depending upon whether the dinoflagellate or nannofossil zonation, respectively, is used; the Valanginian/Hauterivian boundary, as defined by the dinoflagellate zonation, is near reversed-polarity Chron M10N.

Concentration of the rare-earth elements in metalliferous sediments from DSDP Leg 92 holes

DSDP Leg 92 drilled at four sites along an east-west transect at 19°S on the western flank of the East Pacific Rise (EPR), in an area where sediments are essentially a mixture of hydrothermal and biogenic components, with only a minimal contribution of clastic material. Rare-earth element (REE) data on the metalliferous (non-carbonate) fraction of samples ranging in age from ~2 to ~27 Ma indicate the existence of two distinct groups of patterns corresponding to two broad age groups, one <=8 Ma, the other >=10 Ma. Within each group, REE patterns have characteristics which are near-uniform, despite large variations in total REE abundances. Sediments of the younger group are enriched in light REE (LREE) relative to deep bottom waters influenced by the hydrothermal plume extending west from the EPR at 19°S. Sediments of the older groups show further relative LREE enrichment and/or heavy REE (HREE) depletion. Surficial sediments deposited beneath the lysocline have high Sum REE concentrations resulting from slow accumulation rates, and patterns resembling older sediments due to early diagenetic effects. A correlation between the mass accumulation rates (MAR) of Sum REE and Fe + Mn suggests that ferromanganese particulate matter supplied by the hydrothermal plume scavenges REE; during this process the LREE are preferentially removed from plume seawater. The MAR of Fe + Mn shows a general decrease with age above basement, whereas Sum REE concentrations in the metalliferous component increase with age above basement. This supports the Ruhlin and Owen model wherein limited scavenging of REE, due to rapid burial of sediment near the palaeo-axis, leads to low concentrations (but high MAR-values) for the REE. Following deposition and burial of the hydrothermal component, further relative flattening of the REE pattern takes place, probably the result of diagenetic reactions over several million years. Phase partitioning data indicate that the proportion of REE residing in more poorly crystalline phases tends to increase with age (from ~45% to 90% of Sum REE). This suggests that as initial ferromanganese precipitates undergo diagenetic recrystallization, REE are transferred to the poorly crystalline phases, and/or are scavenged from pore waters by these phases. Because of the various modifications to REE patterns apparently produced both in the water column and post-depositional settings, the REE patterns of metalliferous sediments will not reflect fine-scale REE variations in associated oceanic water masses.

Speciation of metals in bottom sediments from the south Kara Sea and Ob and Yenisei estuarine zones

Speciation of Fe, Mn, Zn, Cu, Co, Ni, Cr, Pb, and Cd was studied in 52 samples of bottom sediments collected during Cruise 49 of the R/V "Dmitry Mendeleev" to the estuaries of the Ob and Yenisei rivers and to the southwest Kara Sea. Immediately after sampling the samples were subjected to on-board consecutive extraction to separate metal species according to their modes of occurrence in the sediments: (1) adsorbed, (2) amorphous Fe-Mn hydroxides and related metals, (3) organic + sulfide, and (4) residual, or lithogenic. Atomic absorption spectroscopy of the extracts was carried out at a stationary laboratory. Distribution of Fe, Zn, Cu, Co, Ni, Cr, Pb, and Cd species is characterized by predominance of lithogenic or geochemically inert modes (70-95% of bulk contents), in which the metals are bound in terrigenous and clastic mineral particles and organic detritus. About half of total Mn amount and 15-30% of Zn and Cu are contained in geochemically mobile modes. Spatiotemporal variations in proportions of the metal species in the surface layer of sediments along sub-meridional sections and through vertical sections of bottom sediment cores testify that Mn and, to a lesser extent, Cu are the most sensitive to changes in sedimentation environment. The role of their geochemically mobile species notably increases under reducing conditions.

Organic compounds and bitumen in surface sediments from the Pechora Bay

Detailed geochemical investigations of bottom sediments in the Pechora Bay were carried out under a monitoring regime. The regional geochemical background is characterized. Organic matter of sediments is found to be clastic, formed under the influence of Pechora River run-off, and determined by genetic and lithofacial factors. An application of geochemical methodology is suggested for estimating hydrocarbon contamination of bottom sediments. As an example consequences of the accidental Usinsky oil spill are studied. They are based on analysis of composition of molecular markers. It is shown that increasing technogenic impact on Pechora Bay sediments is fixed only at molecular level and is not disastrous.

Growth rates of late Miocene corals from Crete (Greece)

Modern scleractinian corals are classical components of marine shallow warm water ecosystems. Their occurrence and diversity patterns in the geological record have been widely used to infer past climates and environmental conditions. Coral skeletal composition data reflecting the nature of the coral environment are often affected by diagenetic alteration. Ghost structures of annual growth rhythms are, however, often well preserved in the transformed skeleton. We show that these relicts represent a valuable source of information on growth conditions of fossil corals. Annual growth bands were measured in massive hemispherical Porites of late Miocene age from the island of Crete (Greece) that were found in patch reefs and level bottom associations of attached mixed clastic environments as well as isolated carbonate environments. The Miocene corals grew slowly, about 2-4 mm/yr, compatible with present-day Porites from high-latitude reefs. Slow annual growth of the Miocene corals is in good agreement with the position of Crete at the margin of the Miocene reef belt. Within a given time slice, extension rates were lowest in level bottom environments and highest in attached inshore reef systems. Because sea surface temperatures (SSTs) can be expected to be uniform within a time slice, spatial variations in extension rates must reflect local variations in light levels (low in the level bottom communities) and nutrients (high in the attached reef systems). During the late Miocene (Tortonian-early Messinian), maximum linear extension rates remained remarkably constant within seven chronostratigraphic units, and if the relationship of SSTs and annual growth rates observed for modern massive Indo-Pacific Porites spp. applies to the Neogene, minimum (winter) SSTs were 20°-21°C. Although our paleoclimatic record has a low resolution, it fits the trends revealed by global data sets. In the near future we expect this new and easy to use Porites thermometer to add important new information to our understanding of Neogene climate.

Calcium isotope ratios of porewaters of ODP Leg 204 holes

The calcium isotopic composition of porewaters and authigenic carbonates in the anoxic sediments of a convergent continental margin drilled during Ocean Drilling Program (ODP) provides first insight into the different processes that control Ca geochemistry in clastic marine, organic-rich sedimentary environments. In 4 sites drilled during Leg 204 at Hydrate Ridge (Cascadia Margin, offshore Oregon/USA), sulfate is consumed during anaerobic oxidation of methane and of organic matter via sulfate reduction within the upper meters of the sedimentary section. These reactions promote the precipitation of authigenic carbonates through the generation of bicarbonate, which is reflected in a pronounced decrease in calcium concentration. Although Ca isotope fractionation is observed during carbonate precipitation, Ca concentration in the pore fluids from ODP Leg 204 is decoupled from Ca isotopy, which seems to be mainly controlled by the release of light Ca isotopes that completely overprint the carbonate formation effect. Different processes, such as the release of organically bound Ca, ion exchange and ion pair formation may be responsible for the released light Ca. Deeper within the sedimentary section, additional processes such as ash alteration influence the Ca isotopic composition of the porewater. Two sites, drilled into the deeper core of the accretionary prism, reveal the nature of fluids which have reacted with the oceanic basement. These deep fluids are characterized by relatively high Ca concentrations and low d44/40Ca ratios.

(Supplemet S1) Silicon oxide and Potassium + Sodium oxide from the PACManus hydrothermal area

This study presents a systematic analysis and interpretation of autonomous underwater vehicle-based microbathymetry combined with remotely operated vehicle (ROV) video recordings, rock analyses and temperaturemeasurements within the PACManus hydrothermal area located on Pual Ridge in the Bismarck Sea of eastern Manus Basin. The data obtained during research cruise Magellan-06 and So-216 provides a framework for understanding the relationship between the volcanism, tectonismand hydrothermal activity. PACManus is a submarine felsic vocanically-hosted hydrothermal area that hosts multiple vent fields locatedwithin several hundredmeters of one another but with different fluid chemistries, vent temperatures and morphologies. The total area of hydrothermal activity is estimated to be 20,279m**2. Themicrobathymetrymaps combinedwith the ROV video observations allow for precise high-resolution mapping estimates of the areal extents of hydrothermal activity.We find the distribution of hydrothermal fields in the PACManus area is primarily controlled by volcanic features that include lava domes, thick andmassive blocky lava flows, breccias and feeder dykes. Spatial variation in the permeability of local volcanic facies appears to control the distribution of venting within a field.We define a three-stage chronological sequence for the volcanic evolution of the PACManus based on lava flow morphology, sediment cover and lava SiO2 concentration. In Stage-1, sparsely to moderately porphyritic dacite lavas (68-69.8 wt.% SiO2) erupted to form domes or cryptodomes. In Stage-2, aphyric lava with slightly lower SiO2 concentrations (67.2-67.9 wt.% SiO2) formed jumbled and pillowed lava flows. In the most recent phase Stage-3, massive blocky lavaswith 69 to 72.5wt.% SiO2were erupted throughmultiple vents constructing a volcanic ridge identified as the PACManus neovolcanic zone. The transition between these stages may be gradual and related to progressive heating of a silicic magma following a recharge event of hot, mantle-derived melts.

(Table 1) K-Ar age determinations on biotite from coarse sand within DSDP Sample 72-516F-76-4,107-115

Qualitative petrographic study of selected clastic horizons within the Eocene section of Hole 516F has revealed the presence of abundant fine-grained lithic fragments, probably volcanic, along with coarser fragments of quartz and feldspar apparently derived from a nearby plutonic terrain. In detail, poor sorting, presence of graded bedding, and an abundance of clay suggest these are turbidite horizons locally derived from a mixed volcanic/plutonic terrain, possibly with some direct contribution from contemporary volcanic ash falls. A progressive increase in plutonic versus volcanic components with time is, however, more consistent with an erosional origin for most of this material. Unusual euhedral dark biotite is abundant in several of the lower clastic horizons; it is most easily interpreted as microphenocrysts weathered in situ out of alkalic volcanic ash. Biotite separated from Sample 516F-76-4,107-115 cm, has been dated by the K-Ar method at about 46 Ma. Alkaline volcanoes active on the Rio Grande Rise in the middle Eocene would be the most probable source of this ash and would be consistent with other evidence for potassic, alkaline volcanism along the Rio Grande Rise and at the Tristan da Cunha hot spot.